EP 0 692 562 describes a method for the optical illustration of a fabric consisting of warp and weft threads with a pattern. In this method, the patterns are recorded by a data processing system and displayed on a video screen, the patterns being scanned in from an original. Thereafter, by means of CAD, the warp and weft threads forming the fabric are assigned an intersection diagram, the weaves of which the fabric is to consist being defined. These are known regular weaves, such as linen weaves, satin weaves, twill weaves and basket weaves. Subsequently, the run of the warp and weft threads is determined, the thread-specific parameters and fabric parameters being taken into account. In light of the dynamic behavior and run of warp and weft, the predetermined run of the warp and weft threads is corrected. This corrected warp/weft thread run is illustrated by means of an output unit, for example by means of a video screen or printer. After the correction, various colors are assigned to the individual warp and weft threads.
It is considered a disadvantage that the colors are selected as a function of the colors capable of being illustrated in the output unit, for which purpose a person skilled in the art with experience of weaves is necessary. The output unit is a video screen or a printer which operate on the basis of the ground colors (RGB) and with additive color mixing. It is known, however, that an exact reproduction of an illustration cannot be achieved in the fabric in the ground colors by means of textile weft threads. Since the colors capable of being illustrated by the output unit also contain mixed colors, threads with such mixed colors have to be provided.
DE 44 38 535 discloses a method for the jacquard weaving of a colored cloth. In this method, an image copy to be woven is broken down by means of the screen method known from printing technology. In this method, an original is transferred into a computer by scanning and is displayed on the video screen, a very large number of color shades being present. Subsequently, the colors are reduced to an illustratable or a desired number of colors. Finally, this number of colors is broken down into screen dots having the colors red, yellow and blue and also black and white, the screen dot having the size of a weavable point. After the color breakdown, the weaving program is set up by means of computer technology, each screen dot corresponding to a weaving point. These weaving points are tied off according to the classic jacquard method, that is to say regular weaves with repeat repetitions are used.
The known method has substantial disadvantages. To carry out the method, it is absolutely necessary to have an experienced person skilled in the art with experience of weaves. To be precise, it has become clear that, in the case of woven colored image copies in the colors yellow, red and blue, the color mix is deficient, that is to say they do not have all the color shades of the original. As a rule, corrections are necessary in order to improve the woven image copy. However, corrections of this kind can be carried out only by an experienced person skilled in the art with experience of weaves. In the color breakdown for reprography, it is to be assumed that a color mix occurs in the region between the print colors during the printing operation. In other words, the printed color dots are not clearly delimited, but, instead, the print colors of the adjacent color dots flow partially one into the other in the edge region. In the known method, the illustration is broken down into screen dots which form a weaving point with clear delimitation. The mixing effects are to be generated as a result of the low resolution of the human eye.
It is therefore known that the introduction of jacquard weaving machines has made it possible to produce differently worked patterns, but the production times for more complex patterns are very long and the work to be carried out is extremely complicated. The introduction of the CAD systems in the area of jacquard weaving has led to a considerable simplification of the necessary work and at the same time has reduced the possibility of error during the planning and production of different thread interlacings for the purpose of obtaining various effects. The CAD systems nevertheless also force the workers to carry out special additional work on the images in order then to produce on the final fabric a structure which is as similar as possible to the initial image to be reproduced on the fabric.
In actual fact, the work for preparing the images and their respective treatment, quite apart from the weaving system which is used later, take place as set out below:
First, a color scanning of any desired initial image is carried out (the initial image may be of any desired type, without any restriction); scanning may take place with the aid of a scanner or by means of any other reading system.
The initial image read in this way is visualized by video by means of an appreciable number of colors. Said number of colors is closely related to the performance of the hardware system used and consequently to the configuration of the latter.
In professional configurations, an image with millions of image colors can be read and visualized by video. In actual fact, this is primarily a theoretical performance, since the possibility of visualization of this kind is very rare: normally, images coming from the scanner have thousands of image colors which are selected automatically, during the reading operation, from a spectrum consisting of millions of colors. It is necessary, however, to ensure that each image read by the scanner contains a specific color palette or, put better, a color palette which contains the colors of the image itself in a specific way.
At this point, said image undergoes a first operation for reducing the number of existing image colors, that is to say the initial colors of the initial image. The processes of color reduction may be carried out by means of different methods, such as by the use of special mathematic algorithms which, to be precise, vary on the basis of the way in which the colors are eliminated and/or are replaced by other colors within the image.
In any event, quite apart from the nature of the reduction used and, consequently, of the mathematic algorithm used, the initial image having a large number of initial colors is brought, for example, to 256 reduced colors. This is a step which takes place by virtue of the fact that the images which are subsequently processed by CAD for jacquard textiles do not require a large number of colors, and, as a rule, it is assumed that 256 colors are sufficient for the final objective and for the treatment of the image itself, specifically on the basis of the respective conversion to a pattern for jacquard textiles.
The image treated in this way (reduced in terms of the number of colors), is subsequently transferred into the jacquard CAD system in which all the operations are coordinated which make it possible to convert the image itself into a pattern for jacquard textiles. One of the first steps in this respect is a further reduction of the remaining, already reduced colors. In fact, the number of existing colors is reduced in the image on the basis of the type of fabric and on the basis of the effects to be achieved. Normally, in a fabric pattern, each individual color illustrates a specific type of interlacing and, consequently, a specific type of final effect on the fabric.
At this point, the following steps are linked to the additional work on the available image. On the other hand, the image then available has passed through a considerable series of steps in terms of the reduction, as regards the number of colors and consequently also as regards the information obtained from the image, and, consequently, as soon as the number of selected colors is reached, an image is available which necessarily has to undergo the additional work, so that it is as far as possible similar to the initial image.
The time necessary for the “additional work” on the images is in close interrelationship with the complexity of the pattern. This clearly and markedly implies that, even today, despite the use of highly developed systems, the complex patterns require long times for the complete and final additional work. At the present time, therefore, there is no mathematic algorithm available which makes it possible to convert automatically an image which is read by a scanner (and which is consequently rich in information in terms of the number of existing colors and the nuances, etc.) and at the same time to achieve the exact reproduction of the initial image, without the additional work having to be carried out.
In practice, the different steps described above, which are performed with the purpose of reducing the number of colors present in the read initial image, do not make it possible to maintain, unchanged, the nuances, color shades and different color variations which the image initially has. All this takes place to the disadvantage of the image processing times, but also to the disadvantage of the quality of the final fabric; by “quality” is meant in this case the difference existing between the initial image at the time of reading and the converted image reproduced on the jacquard fabric.
Of course, the number of colors which the image to be reproduced on the jacquard fabric possesses at most may be limited, specifically also by the maximum number of colors of the weft thread which are capable of being used in the weaving machine. Normally, what can be achieved, at least at the present time, in textile weaving machines is that these use up to a maximum of 12 weft thread colors, and therefore the number of reproducible colors is necessarily limited.